Liquid crystal display device

ABSTRACT

A pixel electrode is formed on a TFT substrate, and a gate insulating film is formed thereon. On the gate insulating film, formed is an inorganic passivation film, on which a common electrode having slits is formed. Through-holes are formed in the gate insulating film at areas where the pixel electrode faces the common electrode, and the pixel electrode is not connected to a source electrode in the through-hole. The through-holes are filled with the inorganic passivation film, and the common electrode is formed on the inorganic passivation film at a position corresponding to each through-hole. The pixel electrode faces the common electrode at the position through not the gate insulating film but only the inorganic passivation film, and thus the pixel capacity can be increased. Accordingly, it is possible to prevent changes in the electric potential of the pixel electrode caused by ON/OFF operations.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2011-277235 filed on Dec. 19, 2011, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device, and particularly toan IPS-type liquid crystal display device with excellent viewing anglecharacteristics.

2. Description of the Related Art

In a liquid crystal display panel used for a liquid crystal displaydevice, there are arranged a TFT substrate on which pixels having pixelelectrodes and thin-film transistors (TFTs) are formed in a matrixshape, and an opposed substrate which faces the TFT substrate and onwhich color filters are formed at positions corresponding to the pixelelectrodes of the TFT substrate. In addition, liquid crystal issandwiched between the TFT substrate and the opposed substrate. Thetransmittance of light by liquid crystal molecules is controlled foreach pixel to form an image.

Liquid crystal display devices are flat and light, and thus have beenwidely used in various fields. Small-sized liquid crystal displaydevices have been widely used in cellular phones or DSCs (Digital StillCameras). There is a problem of viewing angle characteristics in theliquid crystal display device. The viewing angle characteristics arephenomena in which brightness and chromaticity are changed when a screenis viewed from the front direction or oblique direction. An IPS (Inplane Switching)-type liquid crystal display device in which liquidcrystal molecules are operated by an electric field in the horizontaldirection is excellent in the viewing angle characteristics.

There are many kinds of IPS-type liquid crystal display devices. Forexample, transmission can be increased by an IPS-type liquid crystaldisplay device in which a common electrode or a pixel electrode isformed in a flat shape, a comb-like pixel electrode or common electrodeis arranged thereon while sandwiching an insulating film, and liquidcrystal molecules are rotated by electric field generated between thepixel electrode and the common electrode. Thus, the IPS-type liquidcrystal display device is currently the mainstream.

In such an IPS type, a TFT is formed first and is covered with apassivation film. On the passivation film, formed are the commonelectrode, the insulating film, the pixel electrode, and the like in aconventional technique. However, the numbers of conductive films andinsulating films in the TFT substrate are reduced due to demand ofreducing the manufacturing costs.

As another example of the IPS type, FIG. 13 of Japanese PatentApplication Laid-Open No. 2009-168878 illustrates a configuration inwhich a common electrode is formed in the same layer as a gateelectrode, and agate insulating film and a comb-like pixel electrode areformed while sandwiching a protective insulating film.

FIG. 11 is a plan view for showing an IPS pixel structure targeted bythe present invention. In FIG. 11, a pixel is formed in an areasurrounded by scanning lines 10 and video signal lines 20. A TFT isformed on the scanning line 10. Specifically, a semiconductor film 103is formed on the scanning line 10 through a gate insulating film 102,and a drain electrode 104 and a source electrode 105 are formed thereon.In addition, the scanning line 10 also serves as a gate electrode. Inthe pixel structure as shown in FIG. 12, a pixel electrode 101 connectedto the source electrode 105 of the TFT is formed in the lowermost layer,a common electrode 107 is formed in the uppermost layer, and liquidcrystal molecules 200 are driven by voltage between the pixel electrode101 and the common electrode 107.

FIG. 12 is a cross-sectional view taken along the line G-G of FIG. 10.In FIG. 12, the gate electrode 10 as the scanning line 10 and the pixelelectrode 101 are formed on the TFT substrate 100 made of glass. Thegate electrode 10 is formed using a laminated film of Al and AlMo alloy,and the pixel electrode 101 is formed using ITO (Indium Tin Oxide). Thegate insulating film 102 is formed while covering the gate electrode 10and the pixel electrode 101.

On the gate electrode 10 and the gate insulating film 102, there isformed the semiconductor film 103 made of a-Si on which the drainelectrode 104 and the source electrode 105 are formed. The sourceelectrode 105 is connected to the pixel electrode 101 through athrough-hole 110 formed in the gate insulating film 102. Thethrough-hole 110 is formed in a horizontally-long shape to reducecontact resistance. An inorganic passivation film

106 is formed while covering the drain electrode 104, the sourceelectrode 105, and the like. On the inorganic passivation film 106, thecommon electrode 107 is formed. Slits 1071 are formed at the commonelectrode 107. If voltage is applied between the pixel electrode 101 andthe common electrode 107, lines of electric force are generated throughthe slits 1071 and liquid crystal molecules 200 are rotated by the linesof electric force. Thus, the amount of light penetrating through theliquid crystal layer can be controlled. As described above, the IPS typeto which the present invention is applied is largely different from theconfiguration of the liquid crystal display device described in JapanesePatent Application Laid-Open No. 2009-168878.

In the configuration shown in FIG. 12, the number of layers to be formedis small, and the number of photolithography steps is also small. Thus,the structure shown in FIG. 12 is excellent in manufacturing costs. Onthe other hand, in the case where pixel capacity is formed between thepixel electrode 101 and the common electrode 107 to suppress a voltageshift caused by changes in gate voltage in the TFT, it isdisadvantageously difficult to increase the pixel capacity.

Specifically, the pixel capacity is formed between the pixel electrode101 and the common electrode 107 in FIG. 12, and the gate insulatingfilm 102 and the inorganicpassivation film 106 are provided between thepixel electrode 101 and the common electrode 107. The thicknesses of thegate insulating film 102 and the inorganic passivation film 106 areabout 300 nm and 500 nm, respectively, and both films are made of SiN.As described above, the pixel capacity is formed through the insulatingfilm with a thickness of 800 nm in total, and thus cannot besufficiently increased. Accordingly, pixel voltage caused by ON/OFF ofgate voltage is largely affected.

An object of the present invention is to solve the above-describedproblems and to realize an inexpensive IPS-type liquid crystal displaydevice in which the number of laminated films is small and pixel voltageis less shifted.

SUMMARY OF THE INVENTION

The present invention overcomes the above-described problems, andconcrete aspects are as follows.

According to the present invention, there is provided a liquid crystaldisplay device including: a TFT substrate on which pixels having pixelelectrodes and TFTs are formed in a matrix shape; an opposed substratehaving color filters; and liquid crystal sandwiched between the TFTsubstrate and the opposed substrate, wherein the pixel electrode isformed on the TFT substrate, a gate insulating film is formed on thepixel electrode, an inorganic passivation film is formed on the gateinsulating film, and a common electrode having slits is formed on theinorganic passivation film; a video signal is supplied to the pixelelectrode from a source electrode of the TFT through a firstthrough-hole of the gate insulating film; a second through-hole isformed in the gate insulating film at a position where the pixelelectrode faces the common electrode, and the pixel electrode and thesource electrode are not connected to each other in the secondthrough-hole; the inorganic passivation film is formed in the secondthrough-hole; and the common electrode is formed on the inorganicpassivation film at an area corresponding to the second through-hole.

According to the present invention, there is provided a liquid crystaldisplay device including: a TFT substrate on which pixels havingtransmissive areas and reflective areas are formed in a matrix shape; anopposed substrate having color filters; and liquid crystal sandwichedbetween the TFT substrate and the opposed substrate, wherein in thereflective area, a pixel electrode is formed on the TFT substrate, agate insulating film is formed on the pixel electrode, and pluralthrough-holes are formed in the gate insulating film; a source electrodeextending from the TFT is formed while covering the gate insulating filmand the plural through-holes; an inorganic passivation film is formedwhile covering the source electrode, and a common electrode having slitsis formed on the inorganic passivation film; the source electrode isconductive with the pixel electrode in the plural through-holes of thegate insulating film; and the source electrode formed on the gateinsulating film and the plural through-holes forms a diffuse reflectionsurface.

According to the present invention, there is provided a liquid crystaldisplay device including: a TFT substrate on which pixels having pixelelectrodes and TFTs are formed in a matrix shape; an opposed substratehaving color filters; and liquid crystal sandwiched between the TFTsubstrate and the opposed substrate, wherein the pixel electrode isformed on the TFT substrate; a gate insulating film is formed whilecovering the periphery of the pixel electrode; no gate insulating filmis provided on the inner side relative to the periphery of the pixelelectrode and an inorganic passivation film is directly formed on thepixel electrode; and a common electrode having slits is formed on theinorganic passivation film.

According to the present invention, there is provided a liquid crystaldisplay device including: a TFT substrate on which pixels having pixelelectrodes and TFTs are formed in a matrix shape; an opposed substratehaving color filters; and liquid crystal sandwiched between the TFTsubstrate and the opposed substrate, wherein the pixel electrode isformed on the TFT substrate, a gate insulating film is formed on thepixel electrode, an inorganic passivation film is formed on the gateinsulating film, and a common electrode having plural slits is formed onthe inorganic passivation film; a video signal is supplied to the pixelelectrode from a source electrode of the TFT through a firstthrough-hole of the gate insulating film; and an area with the gateinsulating film removed is formed at a position where the pixelelectrode faces the common electrode, and the inorganic passivation filmis directly formed on the pixel electrode at the area with the gateinsulating film removed.

According to the present invention, pixel capacity can be increased inan IPS liquid crystal display device in which the number of layers isreduced, and thus changes in the electric potential of a pixel electrodecaused by changes in gate voltage can be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a pixel of a liquid crystal display device in afirst embodiment;

FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1;

FIG. 3 is a cross-sectional view taken along the line B-B of FIG. 1;

FIG. 4 is a cross-sectional view taken along the line C-C of FIG. 1;

FIG. 5 is a plan view of a pixel of a liquid crystal display device in asecond embodiment;

FIG. 6 is a cross-sectional view taken along the line D-D of FIG. 5;

FIG. 7 is a plan view of a pixel of a liquid crystal display device in athird embodiment;

FIG. 8 is a cross-sectional view taken along the line E-E of FIG. 7;

FIG. 9 is a cross-sectional view taken along the line F-F of FIG. 7;

FIG. 10 is a plan view of a pixel of a liquid crystal display deviceaccording to another example in the third embodiment;

FIG. 11 is a plan view of a pixel of a liquid crystal display device ina conventional example; and

FIG. 12 is a cross-sectional view taken along the line G-G of FIG. 11.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, the content of the present invention will be described indetail using embodiments.

First Embodiment

FIG. 1 is a plan view of a pixel part of a liquid crystal display deviceaccording to the present invention. The pixel structure is basically thesame as that explained in FIG. 11. Specifically, a gate insulating film102 shown in FIG. 2 is formed on a scanning line 10 that also serves asa gate electrode, and a semiconductor film 103 is formed on the gateinsulating film 102. On the semiconductor film 103, a drain electrode104 diverged from a video signal line 20 and a source electrode 105 areformed. The source electrode 105 is connected to a pixel electrode 101,formed at the lowermost layer, through a through-hole 110.

An inorganic passivation film 106 shown in FIG. 2 is formed whilecovering the source electrode 105 and the drain electrode 104, and acommon electrode 107 is formed on the inorganic passivation film 106.The common electrode 107 has slits 1071. The common electrode 107 coversthe whole surface of FIG. 1 except the slits 1071. FIG. 1 is largelydifferent from FIG. 11 in that the through-holes 110 are partiallyformed in the gate insulating film 102 covering the pixel electrode 101between the pixel electrode 101 and the common electrode 107, and thedistance between the pixel electrode 101 and the common electrode 107 isshortened at the position of each through-hole 110. The area providedwith diagonal lines in FIG. 11 denotes the through-hole formed in thegate insulating film. The capacity between the pixel electrode 101 andcommon electrode 107 is increased at the position where the distancebetween the pixel electrode 101 and the common electrode 107 isshortened.

In this case, plural through-holes 110 are formed in the gate insulatingfilm 102 at predetermined pitches while being associated with thestriped common electrode 107 sandwiched between the slits 1071. However,it is not essential to form the through-holes 110 while being associatedwith the striped common electrodes 107. The positions and pitches of thethrough-holes 110 may be arbitrarily set unless the orientation ofliquid crystal is affected.

FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1.First, the pixel electrode 101 is formed on a TFT substrate 100 made ofglass. The pixel electrode 101 is formed using ITO by sputtering to havea thickness of, for example, 77 nm to 50 nm. Thereafter, the pixelelectrode 101 is patterned. Next, a film for the scanning line 10 thatalso serves as a gate electrode is formed by sputtering to have athickness of about 220 nm. The scanning line 10 is formed as, forexample, a laminated film in which a lower layer is made of Al having athickness of about 200 nm and an upper layer is made of AlMo alloyhaving a thickness of about 20 nm. As

described above, the pixel electrode 101 and the scanning line 10 of thesame layer are formed on the TFT substrate 100.

Next, the gate insulating film 102 and a-Si as the semiconductor film103 are continuously formed by CVD. It should be noted that n+a-Si (notshown) used for ohmic contact is also formed continuously with a-Si. Thethicknesses of the gate insulating film 102, the a-Si film, and then+a-Si film are about 300 nm, 150 nm, and 50 nm, respectively.

Next, the semiconductor layer 103 is patterned to be in an island shapeas shown in FIG. 1. The semiconductor layer 103 is formed on the gateinsulating film 102, and is patterned by photolithography. Thereafter,the through-hole 110 is formed in the gate insulating film 102. Thesource electrode 105 and the pixel electrode 101 of the TFT can beconnected to each other via the through-hole 110.

In the present invention, the through-holes 110 are formed not only forconnecting the source electrode 105 to the pixel electrode 101. Thethrough-holes 110 are partially formed in the gate insulating film atareas where the pixel electrode 101 faces the common electrode, and thedistance between the pixel electrode 101 and the common electrode 107 isshortened at the position of each through-hole to increase the capacity.The thickness of the gate insulating film is about 300 nm, and thus thedistance between the pixel electrode 101 and the common electrode 107 isshortened by the thickness of the gate insulating film, resulting in anincrease in the pixel capacity.

The video signal line 20, the drain electrode 104, and the sourceelectrode 105 are formed at the same time. Thereafter, the video signalline 20, the drain electrode 104, and the source electrode 105 arereferred to as an SD film in some cases. The SD film is formed usingCrMo by sputtering to have a thickness of about 150 to 200 nm, and ispatterned by photolithography.

Thereafter, the inorganic passivation film 106 is formed by CVD whilecovering the drain electrode 104, the source electrode 105, the gateinsulating film 102, and the like. The inorganic passivation film 106 isformed

using, for example, SiN to have a thickness of as large as about 500 nm.This is because a large thickness is necessary to some extent tofunction as a passivation film. Next, the common electrode 107 isdeposited. The common electrode 107 is formed using ITO by sputtering tohave a thickness of, for example, 77 nm to 50 nm similarly to the pixelelectrode 101. Next, the common electrode 107 formed on the wholesurface is patterned. The patterning of the common electrode 107 isrealized by forming the slits 1071 in the common electrode 107 as shownin FIG. 1 or FIG. 2. Accordingly, after the patterning of the commonelectrode 107, the common electrode 107 exists on the whole surfaceexcept the slits 1071.

When voltage is applied between the pixel electrode 101 and the commonelectrode 107, the lines of electric force as described in FIG. 11 aregenerated, and the liquid crystal molecules 200 are rotated. The amountof light that accordingly penetrates through the liquid crystal layer iscontrolled for each pixel to form an image. It should be noted that anorientation film for initial orientation of liquid crystal formed on thecommon electrode 107 is not illustrated in FIG. 2. This also applies toother cross-sectional views. An opposed substrate (not shown) on whichcolor filters and the like are formed is arranged so as to face the TFTsubstrate 100 of FIG. 2 while sandwiching the liquid crystal layer.

The present invention is characterized in that as shown in FIG. 1 andFIG. 2, the through-holes 110 are partially formed in the gateinsulating film at areas where the pixel electrode 101 faces the commonelectrode 107, and the distance between the pixel electrode 101 and thecommon electrode 107 is shortened at the position of each through-holeto increase the capacity. The thickness of the gate insulating film 102is about 300 nm. If the thickness of the inorganic passivation film 106is about 500 nm, the capacity at the position becomes 8/5 times.

Forming the through-holes 110 in the gate insulating film 102 has noimpact on the capacity at the positions of the slits 1071. In FIG. 1 andFIG. 2, the through-holes 110 are periodically formed in the gateinsulating film 102 at areas where the common electrode 107 faces thepixel electrode 101. This is to prevent irregularities generated byforming the through-holes 110 in the gate insulating film 102 fromseriously having an impact on the orientation of the liquid crystal.

FIG. 3 is a cross-sectional view taken along the line B-B of FIG. 1. InFIG. 3, the pixel electrode 101 is formed on the TFT substrate 100, andthe gate insulating film 102 is formed thereon. The through-holes 110are formed in the gate insulating film 102 at areas where the pixelelectrode 101 faces the common electrode 107. The inorganic passivationfilm 106 is formed on the gate insulating film 102, and the commonelectrode 107 is formed thereon. As shown in FIG. 3, no through-holes110 are formed in the gate insulating film 102 at areas corresponding tothe slits 1071 of the common electrode 107. In FIG. 3, only theinorganic passivation film 106 is provided between the pixel electrode101 and the common electrode 107, and thus the distance between thepixel electrode 101 and the common electrode 107 is shortened, resultingin an increase in the pixel capacity.

FIG. 4 is a cross-sectional view taken along the line C-C of FIG. 1.FIG. 4 is a cross-sectional view of an area where no through-holes 110are formed in the gate insulating film 102. In FIG. 4, the pixelelectrode 101 is formed on the TFT substrate 100, and the gateinsulating film 102 is formed thereon. On the gate insulating film 102,the inorganic passivation film 106 is formed. The common electrode 107is formed on the inorganic passivation film 106. In FIG. 4, the gateinsulating film 102 and the inorganic passivation film 106 are formedbetween the pixel electrode 101 and the common electrode 107. Thus, thepixel capacity in the area is the same as the conventional case, and issmaller than that of FIG. 3. According to the present invention, thethrough-holes 110 are partially formed in the gate insulating film 102at areas where the pixel electrode 101 faces the common electrode 107,and the distance between the pixel electrode 101 and the commonelectrode 107 is shortened. Thus, the pixel capacity can be increased.Further, the through-holes 110 for the gate insulating film 102 can besimultaneously formed with those for

contact between the source electrode 105 and the pixel electrode 101.Thus, the number of manufacturing steps is not increased. As a result,even if the present invention is applied, it is possible to prevent themanufacturing cost from increasing.

Second Embodiment

FIG. 5 shows an example of applying the present invention to asemi-transmissive liquid crystal display device. In FIG. 5, a pixel isprovided in an area surrounded by the scanning lines 10 and the videosignal lines 20. The lower side of the pixel of FIG. 5 is a reflectivearea R, and the upper side thereof is a transmissive area T. In FIG. 5,the configuration of the transmissive area T is the same as that in theconventional example. The through-holes 110 are formed in the gateinsulating film 102 in the reflective area R, and the source electrode105 is formed while covering the gate insulating film 102 and thethrough-holes 110. The cross-section taken along the line B-B of FIG. 5is the same as that of FIG. 3, and the cross-section taken along theline

C-C of FIG. 5 is the same as that of FIG. 4.

In FIG. 5, the source electrode 105 is formed on the entire reflectivearea to serve as a reflective electrode. The source electrode 105 ismade of CrMo, and thus is sufficient in reflection characteristics. InFIG. 5, the through-holes 110 of the gate insulating film 102 are formedat pitches smaller than those in the case of the first embodiment.Accordingly, the surface of the source electrode 105 formed on the gateinsulating film 102 and the through-holes 110 is uneven. Thus, thereflective electrode formed of the source electrode 105 is configured tohave not a mirror surface but a diffuse reflection surface by whichlight can be reflected in a wide range.

In the embodiment, the extended source electrode 105 is made uneven toform the diffuse reflection surface. Thus, the through-holes 110 areformed in the gate insulating film 102 at areas corresponding to theslits 1071 of the common electrode 107. If the through-holes 110 areformed in the gate insulating film 102 at areas corresponding to theslits 1071, the pixel capacity is not increased. However, the diffusereflection surface can be more advantageously formed. It should be notedthat the positions of the through-holes 110 of the gate insulating film102 are shifted from the striped common electrode 107 sandwiched betweenthe slits 1071. Accordingly, the diffuse reflection surface of thesource electrode 105 can be more advantageously formed.

FIG. 6 is a cross-sectional view taken along the line D-D of FIG. 5. InFIG. 6, the gate insulating film 102, the drain electrode 104, and thesource electrode 105 are formed on the scanning line 10 that also servesas a gate electrode to configure a TFT. The left side near the TFT inthe display area is the reflective area R. The through-holes 110 areformed at small pitches in the gate insulating film 102 formed on thepixel electrode 101 in the reflective area R. The source electrode 105extends while covering the plural through-holes 110. The right side ofFIG. 6 is the transmissive area T. In this area, the gate insulatingfilm 102 is formed while covering the pixel electrode 101 as similar tothe conventional case.

The inorganic passivation film 106 is formed while covering the TFT, thesource electrode 105, the gate insulating film 102 and the like. On theinorganic passivation film 106, formed is the common electrode 107. InFIG. 6, only the inorganic passivation film 106 is provided between thesource electrode 105, namely, the pixel electrode 101 and the commonelectrode 107 on the side of the reflective area R, and thus thecapacity is large. On the other hand, the inorganic passivation film 106and the gate insulating film 102 are provided between the pixelelectrode 101 and the common electrode 107 in the transmissive area T,and thus the capacity is smaller than that in the reflective area R.However, the pixel capacity can be increased in the reflective area R,and thus the pixel capacity as the entire pixel can be increased.

In the embodiment, the reflective electrode for isotropically reflectinglight is formed by forming the plural through-holes 110 in the gateinsulating film 102. Thus, a step of forming the reflective electrode isnot added. Further, only one layer of the inorganic passivation film 106is provided between the source electrode 105, namely, the pixelelectrode 101 and the common electrode 107 in the reflective area R, andthus the pixel capacity can be increased in the semi-transmissive liquidcrystal display device.

Third Embodiment

FIG. 7 is a plan view for showing a third embodiment of the presentinvention. In FIG. 7, a pixel is provided in an area surrounded by thescanning lines 10 and the video signal lines 20. FIG. 7 is differentfrom FIG. 1 of the first embodiment in that the gate insulating film 102is widely removed in the pixel area. In FIG. 7, the area surrounded by adotted line is a gate insulating film removed area 120. The sourceelectrode 105 extends to the gate insulating film removed area 120 toconduct the pixel electrode 101 and the source electrode 105.

FIG. 8 is a cross-sectional view taken along the line E-E of FIG. 7. InFIG. 8, the gate insulating film 102 covers the scanning line 10 thatalso serves as a gate electrode and an end of the periphery of the pixelelectrode 101. However, the inner area thereof is widely removed. In anarea where the gate insulating film 102 is removed, only the inorganicpassivation film 106 is provided between the pixel electrode 101 and thecommon electrode 107, and thus the pixel capacity is larger than that inthe conventional example or the first embodiment.

FIG. 9 is a cross-sectional view taken along the line F-F of FIG. 7. InFIG. 9, the pixel electrode 101 is formed on the TFT substrate 100. Thegate insulating film 102 is formed on the pixel electrode 101. However,the gate insulating film 102 is widely removed on the pixel electrode101, and is provided only at ends and outsides of the pixel electrode101. The video signal lines 20 are formed on the gate insulating films102 outside the pixel electrode 101.

The inorganic passivation film 106 is formed while covering the videosignal lines 20, the gate insulating films 102, and the pixel electrode101. The common electrode 107 having the slits 1071 is formed on theinorganic passivation film 106 in the pixel area. In FIG. 9, only theinorganic passivation film 106 is formed between the pixel electrode 101and the common electrode 107 in the pixel area, and thus the pixelcapacity is large.

However, a step of the common electrode 107 becomes high around the gateinsulating film removed area 120 in the configuration of the thirdembodiment. Specifically, the height of the step is equal to the heightsof the gate insulating film 102 and the video signal line 20. If thestep of the common electrode 107 is high, a step of an orientation film(not shown) formed thereon also becomes high. Accordingly, domains ofliquid crystal easily occur in the area, possibly leading todeterioration in image quality.

In order to prevent this problem, the gate insulating films 102 are leftaround the pixel electrode 101 as shown in FIG. 9 in the thirdembodiment. Accordingly, the height of the step of the common electrode107 can be reduced by at least the thickness of the pixel electrode 101.As described above, only the inorganic passivation film 106 is providedbetween the pixel electrode 101 and the common electrode 107 in mostareas except the periphery of the pixel electrode 101 in theconfigurations of FIG. 7 to FIG. 9. Thus, an increase

in the pixel capacity has an extremely great effect.

FIG. 10 shows a modified example of the embodiment. In FIG. 10, thethrough-holes 110 are formed in the gate insulating film 102 while beingassociated with the striped common electrode 107 between the slits 1071.In FIG. 10, the large capacity can be formed in substantially the entirearea of two striped common electrodes 107, and thus large capacity canbe formed as the entire pixel. The cross-section taken along the lineC-C of FIG. 10 is the same as that of FIG. 4. The third embodiment isdifferent from the first embodiment in that the large through-holes 110are continuously formed in the gate insulating film 102 at areascorresponding to the pixel electrode 101.

Further, no through-holes 110 are formed in the gate insulating films102 corresponding to the both sides of the common electrode 107 in theconfiguration of FIG. 10. Thus, large steps generated by the both of thevideo signal lines 20 and the gate insulating films 102 are not formed.The steps in the areas of FIG. 10 are only steps generated by the videosignal lines 20. Accordingly, the problem of occurrence of domains ofliquid crystal is eased as compared to the configuration of FIG. 7.

What is claimed is:
 1. display device comprising: a first substrate; a first electrode and a thin film transistor on the first substrate; a second electrode over the first electrode; and an insulating film between the first electrode and the second electrode, wherein the thin film transistor has a source electrode which is electrically connected to the first electrode, wherein the insulating film has a first area, a second area, and a third area, and wherein a thickness of the first area of the insulating film is larger than a thickness of the second area of the insulating film and the third area of the insulating film, the second area of the insulating film and the third area of the insulating film have the same thickness.
 2. The display device according to claim 1, wherein the source electrode and the first electrode are connected at the second area of the insulating film, wherein the source electrode and the first electrode are not connected at the third area of the insulating film.
 3. The display device according to claim 1, wherein the second electrode has a slit.
 4. The display device according to claim 1, wherein the insulating film comprises an inorganic film, wherein the inorganic film is formed directly on the first electrode.
 5. The display device according to claim 3, wherein the third area of the insulating film is not opposed to the slit.
 6. A display device comprising: a first substrate; a first electrode and a thin film transistor on the first substrate; and a second electrode on the first electrode which is insulated from the second electrode, wherein the thin film transistor has a source electrode which is electrically connected to the first electrode, wherein the first electrode has a first area and a second area, wherein a distance between the first electrode and the second electrode in the first area is larger than a distance between the first electrode and the second electrode in the second area.
 7. The display device according to claim 6, wherein the second electrode has a plurality of slits.
 8. The display device according to claim 6, wherein the at least one first area comprises a plurality of first areas and the at least one second area comprises a plurality of second areas.
 9. A display device comprising: a first substrate; an insulating film, scanning lines and video signal lines crossing the scanning lines on the first substrate; and a first part surrounded by the scanning lines and the video signal lines, wherein the insulating film has a first area, a second area, and a third area in the first part, wherein a thickness of the first area of the insulating film in the first part is larger than a thickness of the second area of the insulating film in the first part, the second area of the insulating film in the first part and the third area of the insulating film in the first part have the same thickness.
 10. The display device according to claim 9, wherein the insulating film is overlapped with the scanning lines and the video signal lines.
 11. The display device according to claim 9, further comprising, a thin film transistor, a first electrode, and a second electrode on the first substrate, wherein the insulating film is in direct contact with at least one of the first electrode and the second electrode, wherein the thin film transistor has a source electrode which is electrically connected to the first electrode.
 12. The display device according to claim 11, wherein the source electrode and one of the first electrode and the second electrode are connected at the second area of the insulating film in the first part, wherein the source electrode and one of the first electrode and the second electrode are not connected at the third area of the insulating film in the first part.
 13. The display device according to claim 11, wherein one of the first electrode and the second electrode has a slit. 